Ethylene .alpha.-olefin elastomeric polymers (EP) have been widely used in extrusion applications such as electrical insulation for decades. These products are expected to provide an extrusion surface free of melt fracture. While this can be accomplished readily by the introduction of long chain branches in an EPDM through the diene, copolymers have to rely on other structural features. For example, use of multi-sited Ziegler-Natta catalyst will provide a very broad molecular weight distribution (MWD) (Mw/Mn&gt;20) suitable for extrusion processing.
Metallocene or single sited catalyst produced elastomeric polymers will generally have a draw back in processability when extruded compared to the previously used elastomeric polymers based on multi-sited Ziegler-Natta produced elastomeric polymers. This drawback stems from the narrow MWD (Mw/Mn about 2), characteristic of such polymers. This MWD effect manifests itself through a lack of shear sensitivity, i.e., shear sensitivity being generally lower viscosity at higher shear rates.
The challenge in providing a metallocene catalyzed elastomeric polymer, with its attendant benefits, to the extrusion and/or electrical industry, is that these materials are generally known by those of ordinary skill in the art as narrow CD, narrow MWD elastomeric polymers. Based on such a characterization, those of ordinary skill in the art would not tend to make these metallocene catalyzed elastomeric polymers their choice for extrusion processes, because to do so would be to select a material whose characteristics are opposed to those outlined above as fitting extrusion processes.
There is a commercial need, therefore, for a metallocene catalyzed elastomeric polymer material which, when compounded, can provide a compound with processability or extrudability equal to a Ziegler-Natta (Z-N) analog.